The first email was sent between the two machines shown in this photograph. They were (obviously) side-by-side, but the only connection between them was through the ARPANET. In the foreground is BBN-TENEXA (BBNA for short). Host names in 1971 had no .com or dot anything; DNS came along later. BBNA was the machine on which the first email was received. In the background is BBN-TENEXB (BBNB) from which the first email was sent. On the left, foreground, is the Teletype KSR-33 terminal on which the first email was printed. Immediately behind and largely obscured is another KSR-33 on which the first email was typed.
BBNA was a Digital Equipment Corporation KA10 (PDP-10) with 64K (36-bit) words of (real magnetic) core memory. In modern measure, that's 288 KBytes. BBNB was smaller with only 48K words. Both machines ran the TENEX time-sharing monitor.
